1. Field of the Invention
This invention relates to production of acetic acid, by reaction of a feedstock of a methyl ester, methanol and water, with carbon monoxide, at a predetermined pressure and temperature, in the presence of a suitable catalyst.
2 Description of the Prior Art
Acetic acid may be prepared from a feedstock containing methyl esters by a process which involves three steps. This process requires acid hydrolysis of a methyl ester such as methyl acetate into acetic acid and methanol, followed by separation of methanol and water by distillation, and subsequent carbonylation of the separated methanol with carbon monoxide to form additional acetic acid. However, the process is uneconomical because the high latent heats of vaporization of both water and methanol requires large quantities of steam and cooling water during the separation step.
U.S. Pat. No. 3,769,329 issued to Frank E. Paulik, et al disclosed a process for preparation of acetic acid by the carbonylation reaction of an alcohol, ester, or ether with carbon monoxide in the presence of a rhodium catalyst. In that process the reaction mixture is flash boiled to recover the crude product from the catalyst.
However, such a rhodium catalyst will form inactive precipitates of rhodium compounds under a low carbon monoxide partial pressure and high temperature and the reaction rate decreases. As such, the flash boiling step may only be carried out at lower temperatures. This in turn results in a lower concentration of acetic acid in the crude product and then large quantities of steam and cooling water are required in the purification operations. Meanwhile, since rhodium is an expensive precious metal, the overall production cost of the acid is high.
Furthermore, in the above prior art if the concentration of the methyl compound e.g., methyl iodide, methanol, or methyl acetate, is too high, the catalyst loses its activity; and if the water concentration is too low or the carbon monoxide partial pressure is too low the rhodium catalyst precipitates. Thus the window of operation conditions in that invention is narrow and the control is difficult.
Naglieri, in U.S. Pat. No. 4,356,320, disclosed an improved carbonylation process for the production of acetic acid using less expensive nickel, or a nickel compound, in place of rhodium. However, the new process still required methanol feedstock as the source of the methanol reactant in the carbonylation process.
Accordingly, it is an object of this invention to provide a new process for the industrial production of acetic acid.
Another object of the invention is to provide a process for making acetic acid which uses a feedstock of a methyl ester, water and an alcohol.
Among the other objects of the invention is to provide a carbonylation process for the production of acetic acid using a catalyst of nickel or a nickel compound, with or without molybdenum, containing phosphorus compounds as ligands, and an iodine promoter.
Yet another object of the invention is to provide a process for the production of acetic acid in which the catalyst remains in a dissolved state and active while carrying out the step of recovery of the acetic acid from the reaction product, at high temperatures and low carbon monoxide partial pressures.
These and other objects of the invention will be made apparent from the following description hereinafter.